A common type of electrical submersible pump comprises a centrifugal pump suspended on a string of tubing within a casing of the well. The pump is driven by a downhole electrical motor, normally a three-phase AC type. A power line extends from a power source at the surface alongside the tubing to the motor to supply power.
Typically the power line is made up of two sections, a motor lead and a power cable. The motor lead has a plug on its lower end that secures to a receptacle known as a “pothead” at the upper end of the electrical motor. The motor lead has three conductors that are insulated and located within a single elastomeric jacket that is extruded around the assembled insulated conductors. Metallic outer armor may wrap around the jacket of the motor lead to avoid damage to the motor lead while running the pump assembly into the well. The motor lead extends upward beyond the pump, for example from 10 to 80 ft. The total of the motor lead and pothead is known as the motor lead extension (MLE). The lead could exceed 80 ft or be shorter than 10 ft depending on the application. A splice connects the motor lead to the power cable. The motor lead is flat and smaller in dimension than the power cable so that it can pass between the pump assembly and the casing.
The power cable comprises three conductors, each having one or more layers of insulation. An elastomeric jacket is usually extruded over the assembled conductors. In some cases, the insulated conductors are encased in lead. The insulated conductors are arranged either in a flat side-by-side configuration, or in a round configuration spaced 120 degrees apart from each other relative to a longitudinal axis of the power cable. A metallic armor is typically wrapped around the jacket to form the exterior of the power cable.
In some wells, the formation temperature is quite hot. Also, the motor generates heat. At least one of the insulation layers of each conductor may be formed of a polymer that is resistant to high temperature degradation. However, current high temperature polymer materials may not be capable of withstanding the high temperatures and harsh environments in some wells. If the insulation degrades, a short could result that would require the pump assembly to be pulled and replaced.
In some wells, rather than suspending the pump assembly on the production tubing through which the pump discharges, coiled tubing is employed. Production tubing is made up of sections of pipe secured together by threads. Coiled tubing comprises metal tubing that is unreeled from a reel at the surface while the pump assembly is being installed. The coiled tubing encases the entire power cable and provides sufficient strength to support the weight of the pump. The pump discharges into a casing or liner surround the coiled tubing.